1. Technical Field
The present invention relates to a surface treatment method for metal parts.
2. Related Art
Spacers interposed between magnetic discs of a hard disc device are conventionally formed into a predetermined shape by pressing, cutting or the like, and barrel polishing is thereafter carried out for the spacers in order that burrs may be removed from the spacers. In the barrel polishing, finely divided or fine powder is produced from the spacers and abrasives, and a pressing force applied during polishing causes the fine powder to pierce into surfaces of the spacers. Accordingly, ultrasonic cleaning is carried out during or after the polishing in order that the fine powder may be removed from the spacers. However, micron-sized recesses and grooves may remain on the surfaces of the spacers due to the polishing. The fine powder enters into the recesses and the grooves, so that it would be difficult to completely remove the fine powder by the ultrasonic cleaning. In particular, since fine powder of alumina (Al2O3) abrasive grain is so hard that alumina cannot easily be removed completely, alumina is regarded as unfavorable in industry, and process control by use of alumina-free abrasives is desired.
Japanese Patent Application Publication No. JP-A-H10-074350 discloses, as a countermeasure, a surface treatment method in which a metal or ceramic film is formed on the surfaces of the spacers so as to confine the fine powder adherent to the surfaces of the spacers inside the film. According to this method, the fine powder can be prevented from being exposed on the surfaces of the spacers while remaining.
However, the above-described surface treatment method confining the fine powder adhered to the spacer surfaces inside the film has a problem of high costs.